1. Field of the Invention
The present invention generally relates to optical modules, and more particularly to an optical module mounted with an optical element such as a light receiving element.
2. Description of the Related Art
Optical modules are used in various applications, including cameras for vehicles, security systems and the like. The optical module is made up of a substrate, an optical element that is mounted on the substrate. For example, the optical element is a CCD or a CMOS device.
There are demands to decrease the size of the optical module without deteriorating the reliability of the optical module. For this reason, the optical element must be accurately positioned relative to the substrate, and electrical connections between the optical element and other parts on the substrate must not easily deteriorate with time or in response to externally applied shock.
Conventionally, the optical element is mounted on the substrate manually, by manually soldering terminals of the optical element to corresponding terminals on the substrate.
But when the optical element is mounted on the substrate manually, it is difficult to accurately position the optical element three-dimensionally relative to the substrate surface. If the optical element is not mounted in a parallel state relative to the substrate surface, an optical axis of the optical element will become inclined from a normal to the substrate surface, to thereby deteriorate the performance of the optical module.
The optical element may be mounted on the substrate so that the bottom surface of the optical element makes contiguous contact with the substrate surface, to ensure the optical element in a parallel state relative to the substrate surface. But when the terminals of the optical element are soldered to the corresponding terminals on the substrate, the solder easily cracks to deteriorate the reliability of the optical module. The crack in the solder is generated with time when temperature changes occur, because the coefficients of thermal expansion are usually different between the materials used for the substrate and the optical element, and the contiguous contact between the optical element and the substrate will not allow the stress caused by the difference between the coefficients of thermal expansion to be absorbed. Moreover, the crack in the solder is generated in response to an externally applied shock, because the contiguous contact between the optical element and the substrate will not allow the shock to be absorbed.
Furthermore, when the terminals of the optical element are manually soldered to the corresponding terminals on the substrate, it is difficult to uniformly control the amount of solder applied to each terminal, particularly since the intervals of the terminals become extremely short as the size of the optical module is reduced. Consequently, it is difficult to uniformly control the reliability of the optical modules. In addition, the manual soldering makes it difficult to manufacture the optical modules with a high efficiency and at a low cost.